1. Field of the Invention
The present invention relates to a device for cooling a reactor vessel under a severe accident condition and, more particularly, to such a device having spray nozzles respectively positioned adjacent a vessel bottom, an upper head, and a body of the reactor vessel for cooling the reactor vessel and preventing melt-through.
2. Description of the Invention
In a commercial nuclear reactor, heat, from which steam and ultimately electricity are generated, is produced by fissioning of a fissible material, such as enriched uranium, contained in a reactor core which is, in turn, contained within the reactor vessel. The reactor vessel includes a flanged closure head bolted atop a flanged reactor body; the reactor vessel is entirely contained within a containment building for containing any unlikely radiation leakage within the containment building should an accident occur. A coolant, typically water, flows through the reactor core for controlling the nuclear reaction and for conveying the generated heat away from the reactor vessel.
Due to safety concerns, various safety mechanisms are present for safely shutting down the nuclear process and for containing any radiation within the reactor vessel or, as a final safety device, within the containment building. One safety concern is to contain the fissible material if the water is completely drained from the reactor vessel leaving the fissible material uncovered. This would cause the fissible material to melt which, in turn, would cause the reactor vessel body to structurally fail, generally referred to as melt-through, if the fissible material or the reactor vessel, or both, are not cooled by water.
Although not particularly directed to melt-through, in a pressurized water reactor system, one safety mechanism, a containment spray system (CSS), is for limiting the pressure in the containment building, as is well known in the art. The CSS sprays a sodium hydroxide solution of borated water into the containment building and, thus, onto the reactor vessel for limiting the pressure inside the containment building and, as a secondary effect, cooling the reactor vessel.
Although the present systems for shutting down and containing the nuclear process are satisfactory, there are areas where, due to improved technology or the like, the extent of protection for severe accidents may be expanded, for example by preventing melt-through of the reactor vessel.
Consequently, a need exists for an improved device for cooling the reactor vessel.